Methods and systems for treating arrhythmias using a combination of vibrational and electrical energy

ABSTRACT

Methods and apparatus for cardiac pacing, cardioversion and defibrillation rely on delivering ultrasonic or other vibrational energy in combination with electrical energy to the heart, usually after the onset of an arrhythmia. A vibrational transducer and suitable electrical contacts may be combined in a single housing or distributed among various housings, and will usually be implantable so that the vibrational transducer can be directed at a target portion of the heart. Alternatively, external systems comprising the vibrational transducer and electrical contacts are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.10/869,242, now U.S. Pat. No. 7,184,830, filed Jun. 15, 2004, whichclaimed the benefit of provisional U.S. Application Ser. No. 60/496,179,filed Aug. 18, 2003, the full disclosures of which are incorporatedherein by reference.

The disclosure of the present application is also related to thefollowing applications: U.S. patent Ser. No. 10/869,776 filed Jun. 15,2004 (now U.S. Pat. No. 7,006,864); U.S. patent application Ser. No.10/869,631, filed Jun. 15, 2004; and U.S. patent application Ser. No.10/869,705, filed Jun. 15, 2004, (now U.S. Pat. No. 7,050,849), the fulldisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and treatmentmethods. More particularly, the present invention relates to methods andapparatus for treating cardiac arrhythmias with vibrational energy.

Cardiac arrhythmias, including ventricular tachycardias and ventricularfibrillation, are a leading cause of morbidity and death in Westernsocieties. A very successful technique for treating such arrhythmias isgenerally referred to as “ventricular cardioversion and defibrillation,”where electrical energy is applied across the chest to synchronizecardiac rhythm. The use of external cardioversion and defibrillationequipment, i.e. where electrode paddles are placed externally on thechest and where relatively high electrical energy is applied, has beenvery effective, but of course requires the availability of both theequipment and an operator capable of using the equipment. More recently,implantable cardioverter defibrillator (ICD) devices have come into use,which are programmed to automatically intervene after the onset of anarrhythmia. ICD's stabilize the cardiac rhythm by deliveringcardioversion, defibrillation, and pacing therapies as needed. SuchICD's have been shown to improve survival and have become the standardof therapy in patients at risk.

ICD's, however, do suffer from certain disadvantages. At present, ICDdesigns require one or more electrical leads to be implanted on orwithin the heart in order to provide pacing, cardioversion anddefibrillation energy. Such lead placement requires skilled personneland subjects the patient to radiation during the implantation procedure.The implanted leads are subject to failure and may cause cardiacperforation, thrombo-occlusion, and infection. Lead failure due tofracture or insulation break has been reported to occur in a significantfraction of the patient population after several years. In contrast,implanted leads used for bradycardia pacing have better reliability thanICD leads due to reduced electrical energy carrying requirements. Itwould be desirable to be able to use pacing leads, carrying less energy,to defibrillate patients and improve lead reliability. Present ICD'salso require a relatively long time to charge capacitors, typically from10-15 seconds, potentially delaying treatment after a potentially lethalarrhythmia is detected. Delay in treatment also requires higher energydelivery to be successful. Moreover, many patients who have receivedICD's find that the electric shocks are painful, and the unpredictablenature of the ICD firing can cause anxiety and fear.

Atrial fibrillation is another form of cardiac arrhythmia and ischaracterized by rapid and disorganized electrical activity in both theleft and right atria of the heart. Atrial fibrillation causes absence ofatrial contraction and often atrial enlargement. Although not directlylethal, atrial fibrillation is associated with thrombus formation in theatrial appendages and has the potential for causing thrombolic stroke.The lack of coordinated atrial contraction can reduce cardiac outputwhich can exacerbate other heart conditions. Patients in atrialfibrillation may experience heart failure, chest pain, fatigue, lightheadedness, and shortness of breath. The rapid and irregular heartbeatand palpitations associated with atrial fibrillation can be verydistressing to patients. Thus, while atrial fibrillation is not directlyfatal, it can be very distressing to patients and has a potential forincreasing mortality from other conditions.

Atrial fibrillation may be controlled using the same techniques appliedto ventricular arrhythmias, including both external defibrillators andICD devices. The shortcomings of both these approaches discussed above,however, are even more of a concern for patients suffering from atrialfibrillation since patients are conscious and alert. Moreover, atrialfibrillation events often occur more frequently than ventriculararrhythmias, and patients are often unwilling to tolerate the painassociated with either external defibrillation or the use of ICD deviceson such a frequent basis.

For these reasons, it would be desirable to provide improved methods anddevices for the treatment of cardiac arrhythmias, including bothventricular arrhythmias and atrial arrhythmias. In particular, it wouldbe desirable to provide such methods and systems for reducing the levelof electrical energy required in order to achieve defibrillation andthus reduce the associated pain and shock. Particularly, it would bedesirable if such methods and systems could be applied to both externaldefibrillation and the use of ICD devices. At least some of theseobjectives will be met by the inventions described below.

2. Description of the Background Art

Patents describing the treatment of arrhythmias using mechanical shocktherapy include U.S. Pat. Nos. 6,408,205; 6,330,475; 6,110,098; and5,433,731. See also U.S. Pat. Nos. 6,539,262; 6,439,236; 6,233,484;5,800,464; 5,871,506; 5,292,338; 5,165,403; and 4,651,716, as well as WO03/070323 and WO 99/61058. Medical publications discussing the effectsof ultrasound energy and/or mechanical action on the heart include:

-   The Antiarrhythmics Versus Implantable Defibrillators (AVID)    Investigators: A comparison of antiarrhythmic drug therapy with    implantable defibrillators in patients resuscitated from near fatal    ventricular arrhythmias. N Engl J Med 1997; 337: 1576-1583.-   Bardy G H, Cappato R., Smith W M, Hood M, Rissmann W J, Gropper C M,    Ostroff H. The totally subcutaneous ICD system (The S-ICD). PACE.    2002; 24,578.-   Camm A J, Murgatroyd F D. Nonpharmaceutical treatment of atrial    fibrillation. In Atrial Fibrillation. Facts from Yesterday—Ideas for    Tomorrow. Futura Publishing Company, Inc., Armonk, N.Y., 1994.-   Dalecki D, Keller B B, Raeman C H, Carstensen E L. Effects of pulsed    ultrasound on the frog heart: I. Thresholds for changes in cardiac    rhythm and aortic pressure. Ultrasound in Med. & Biol. 1993;    19:385-390.-   Dalecki D, Keller B B, Carstensen E L, Neel D S, Palladino J L,    Noordergraaf A. Thresholds for premature ventricular contractions in    frog hearts exposed to lithotripter fields. Ultrasound in Med. &    Biol 1991; 17:341-346.-   Dalecki D, Raeman C H, Carstensen E L. Effects of pulsed ultrasound    on the frog heart: II. An investigation of heating as a potential    mechanism. Ultrasound in Med. & Biol. 1993; 19:391-398.-   Ellenbogen K A, Wood M A, Shepard R K, Clemo H F, Vaughn T, Holloman    K, Dow M, Leffler J, Abeyratne A, Verness D. Detection and    management of an implantable cardioverter defibrillator lead    failure. JACC. 2003; 41:73-80.-   Feldman A and Bristow M. Comparison of medical therapy,    resynchronization and defibrillation therapies in heart failure    trial (COMPANION). Presented at ACC 2003 Late Breaking Clinical    Trials.-   Franz M R. Mechano-electrical feedback in ventricular myocardium.    Cardiovascular Research. 1996; 32:15-24.-   Gibbons R J, Antman E M, Alpert J S, Gregoratos G, Hiratzka L F,    Faxon D P, Jacobs A K, Fuster V, Smith S C Jr. ACC/AHA/NASPE 2002    guideline update for implantation of cardiac pacemakers and    antiarrhythmia devices: a report of the American College of    Cardiology/American Heart Association Task Force on Practice    Guidelines (ACC/AHA/NASPE Committee to Update the 1998 Pacemaker    Guidelines). Circulation. 2002; 106:2145-2161.-   Hu H, Sachs F. Stretch-activated ion channels in the heart. J. Mol.    Cell Cardiol. 1997; 29:1511-1523.-   Kohl P, Hunter P, Noble D. Stretch-induced changes in heart rate and    rhythm: clinical observations, experiments and mathematical models.    Progress in Biophysics & Molecular Biology. 1999; 71:91-138.-   Kohl P, Nesbitt A D, Cooper P J, Lei M. Sudden cardiac death by    Commotio cordis: role of mechano-electrical feedback. Cardiovascular    Research. 2001; 50:280-289.-   Kohl P and Ravens U. Cardiac mechano-electric feedback: past,    present, and prospect, Prog. Biophys. Mol. Biol. 2003; 82:3-11.-   Lee K L, Hafley G, Fisher J D, Gold M R, Prystowsky E N, Talajic M,    Josephson M E, Packer D L, Buxton A E. Effect of implantable    defibrillators of arrhythmic events and mortality in the multicenter    unsustained tachycardia trial. Circulation. 2002; 106:233-238.-   Moss A J, Zareba W, Hall W J, Klein H, Wilber D J, Cannom D S,    Daubert J P, Higgins S L, Brown M W, Andrews M L. Prophylactic    implantation of a defibrillator in patients with myocardial    infarction and reduced ejection fraction. N Engl J Med. 2002;    346:877-933.-   Niehaus M, Pirr J, De Sousa M, Houben R, Korte T, Eick O J.    Non-contact cardiac stimulation with focused ultrasound pulses. PACE    2003: 26:1023.-   Nolte S, Doring J H, Frey A. Mechanically induced ventricular    extrasystoles in the isolated perfused guinea-pig heart.    Arzneim.-Forsch/Drug Research. 1987; 37(11): 1025-1029.-   Reiter M J. Effects of mechano-electrical feedback: potential    arrhythmogenic influence in patients with congestive heart failure.    Cardiovascular Research. 1996; 32:44-51.-   Smailys A, Dulevicius Z, Muckus K, Dauksa K. Investigation of the    possibilities of cardiac defibrillation by ultrasound.    Resuscitation. 1981; 9:233-242.-   Tacker, W A. Fibrillation causes and criteria for defibrillation. In    Defibrillation of the heart, Tacker, W A, ed. Mosby-Year Book, Inc.,    St. Louis, Mo., 1994.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods and systems for treating cardiacarrhythmias, including both ventricular and atrial arrhythmias, by thecombined delivery of both electrical energy and vibrational energy tothe heart. It is presently believed that delivery of electrical energyand vibrational energy may induce a variety of mechanisms by which thesame or different mechano-sensitive ion channels are affected toterminate the arrhythmia. When delivered simultaneously, the electricaland vibrational energies may combine to increase the effect onparticular ion channels or to affect different ion channels in differentways. Thus, the improvement with the combined therapy may result from agreater effect on particular myocardial cells than achieved with eithertherapy alone or alternatively by affecting a greater number ofmyocardial cells than could be achieved with either therapy alone, atleast at lower energy levels. Thus, the present invention may achievethe successful termination of arrhythmias using lower electrical and/orvibrational energy levels or may alternatively use the same energylevel(s) with a greater efficiency. The ability to use lower energylevels allows for a number of system improvements, including moreefficient use of batteries, greater margins of safety for treatment, aswell as a reduction in pain. In addition, the methods and systems of thepresent invention may provide electrical and/or vibrational energy forpacing of selected heart chambers. Furthermore, pace termination oftachyarrhythmias, using programmed trains of pacing stimuli atprespecified intervals and durations, rather than higher energyelectrical shock termination, may be enhanced using electrical and/orvibrational energy.

Thus, in a first aspect of the present invention, methods forstabilizing cardiac arrhythmias comprise delivering controlledvibrational energy from a vibrational transducer to the heart and,concurrently and/or successively or alternatively, delivering electricalenergy to the heart, where the vibrational energy and/or electricalenergy are delivered under conditions which terminate the arrhythmia.The vibrational energy and electrical energy may be delivered by eitherimplanted device(s) or external device(s).

The location at which the devices are implanted and/or externallyengaged against the patient's skin will be determined at least in partbased on the particular therapy being applied. For example, for thetreatment of ventricular arrhythmias including both ventricularfibrillation and ventricular tachycardia, the device may be implanted atleast partially under the patient's ribs, at least partially in a gapbetween the patient's ribs, at least partially over the patient's ribsand/or sternum, or in an abdominal region of the patient. The preciselocation will be chosen to optimize delivery of the energy, particularlythe vibrational energy, to the ventricular aspect of the heart. Theelectrical energy will usually be delivered by implantable leadscontaining electrodes extending from the implantable housing whichcontains the vibrational transducer and associated control and powercircuitry. The implantable leads may be placed transvenously to one ormore of the heart's atria or ventricles. The implantable leads may beplaced subcutaneously. Alternatively, the electrical energy could bedelivered in part from subcutaneous electrodes or from electrodes on theimplantable housing.

Externally delivered vibrational energy and electrical energy for thetreatment of ventricular arrhythmias will typically be accomplished byapparatus engaged against the patient's chest. Electrical contacts maybe generally conventional defibrillation electrode pads or paddles. Thevibrational transducer(s) will be located generally over the ventricularregion of the heart along a path which permits penetration of thevibrational energy to the ventricle(s). Alternatively, the vibrationaltransducer(s) may be located within the defibrillation pads or paddles.

For the treatment of atrial arrhythmias, vibrational energy may bedirected from the anterior chest or alternatively the posterior chest.Thus, the apparatus for delivering the vibrational energy may beimplanted at least partially either over the ribs and/or sternum or in agap between the ribs or beneath the ribs in the anterior chest, or overthe ribs in the posterior chest.

The vibrational energy will be delivered under conditions whichsynergize with the electrical energy to either reduce the electricalenergy required to terminate the arrhythmia and/or to enhance theeffectiveness of the termination of the arrhythmia. Preferredcharacteristics for the delivery of the vibrational energy are set forthbelow. The electrical energy may be delivered at conventional powerlevels and under conventional control algorithms as are presentlyemployed with either external defibrillators or implantable cardioverterdefibrillator (ICD) devices. Advantageously, however, the delivery ofvibrational energy according to the present invention will usuallypermit lowering of the electrical energy delivered through theelectrical contacts to the heart. Thus, the pain and inconvenience ofboth external and internal defibrillation associated with electricaldefibrillators may be lessened or eliminated entirely.

Alternatively or optionally, vibrational energy will be delivered toterminate certain specific arrhythmias detected, while electrical energywill be delivered to terminate other specific arrhythmias detected. Asan example, one energy source may be used to accomplish pacing therapy,while the other may be used to accomplish defibrillation therapy. Thiswould be advantageous when an arrhythmia is more responsive to oneenergy source than the other.

Methods according to the present invention will usually further comprisedetecting an onset of an arrhythmia, particularly when delivering thevibrational and/or electrical energy using an implanted device.Particularly for the treatment of ventricular arrhythmias, the automaticdelivery of both the controlled vibrational energy and the electricalenergy in automatic response to detection of the arrhythmia is anadvantage. Alternatively, particularly in the case of the treatment ofatrial arrhythmias, it may be possible to initiate the delivery ofcontrolled vibrational energy and/or electrical energy manually, usingother implanted or external devices. For example, implantable devicescould be programmed to permit initiation of therapy by the patient oranother individual using an external wand or similar device which cantranscutaneously control the implanted circuitry.

Systems according to the present invention for stabilizing cardiacarrhythmias are comprised of a vibrational transducer adapted to delivervibrational energy to the heart, electrical contacts adapted to deliverelectrical energy to the heart, and control circuitry for delivering atleast one of the vibrational energy and the electrical energy to theheart under selected conditions. As described above in connection withthe methods of the present invention, the vibrational transducer and/orthe electrical contacts may be implantable or alternatively may beadapted to externally engage the patient's skin. For implantabledevices, the vibrational transducer will operate under the conditionsdescribed in more detail below. The electrical energy will be deliveredunder conditions generally utilized for implantable cardioverter devicesor preferably, at power levels lower than those conventionally employedfor such implantable defibrillators. Particular electrical energy levelsare set forth in more detail below.

For the external systems of the present invention, the vibrationalenergy levels are generally set forth below. The electrical energy maybe delivered under conditions generally as used in conventional externaldefibrillators, but will more preferably be delivered at energy andpower levels much lower than those employed by conventional externaldefibrillators. Particular electrical power levels are set forth below.

The control circuitry of the systems of the present invention willoptionally include systems for detecting an onset of an arrhythmia andfor automatically activating and synchronizing the delivery ofvibrational energy and/or electrical energy in response to suchdetection. Alternatively, the control circuitry may be configured toallow manual activating and synchronizing the delivery of either or boththe vibrational and electrical energies.

The systems will further be configured to control the order and durationof delivery of both the vibrational energy and the electrical energy.Usually, the vibrational energy and electrical energy will be deliveredat least partly simultaneously. Under particular circumstances, however,it may be advantageous to commence the delivery of the vibrationalenergy prior to the delivery of the electrical energy or, alternatively,initiate the delivery of the electrical energy prior to the delivery ofthe vibrational energy.

The systems may be configured in a variety of ways. Usually, thevibrational transducer, the electrical contacts, and the controlcircuitry will be packaged in or as part of a common housing.Alternatively, any one or more of these components may be packagedseparately in housings. The particular configurations for thevibrational transducer has been set forth above, where the vibrationaltransducer will optionally further be adapted to preferentially deliverthe vibrational energy to either the ventricular region of the heart,the atrial region of the heart, or in some instances both, depending onthe intended use of the system. In specific embodiments, the controlcircuitry further comprises a power amplifier, an impedance matchingcircuit, and a signal generator, optionally for each segment of thevibrational transducer in the case where the transducer aperturecomprises multiple individual elements. Usually, for implantabledevices, the control circuitry will further comprise a battery or aremotely rechargeable battery and optionally further a transmitterand/or receiver for communication with an external controller. In allimplantable systems, the electrical contacts will typically comprisesubcutaneously and/or transvenously implantable leads which extend fromthe housing to the heart or are a part of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic illustrations of a longitudinalvibrational wave traveling through biological tissue. FIG. 1A shows thepulse repetition period (PRP) while FIG. 1B shows the details of asingle burst or pulse.

FIG. 2 is a schematic illustration of the relationship between frequency(wavelength) and focus of an ultrasonic beam.

FIG. 3 illustrates high frequency beams from convex, flat, and concaveapertures which form divergent, mildly focused, and sharply focusedbeams, respectively.

FIGS. 4A and 4B illustrate the anatomy in which the vibrationaltransducers of the present invention are to be implanted.

FIGS. 5A-5C illustrate alternative implantation sites for thevibrational transducers and transducer assemblies of the presentinvention.

FIG. 6 illustrates a first embodiment of a vibrational transducerassembly constructed in accordance with the principles of the presentinvention.

FIG. 7 illustrates a second embodiment of a vibrational transducerassembly constructed in accordance with the principles of the presentinvention.

FIG. 8 illustrates a third embodiment of a vibrational transducerassembly constructed in accordance with the principles of the presentinvention.

FIGS. 9A and 9B illustrate a circuit configuration (FIG. 9A) and serialburst pattern (FIG. 9B) which would be suitable for operating thevibrational transducer assembly of FIG. 8.

FIG. 10 is a block diagram showing an embodiment of the controlcircuitry implementation of the present invention.

FIG. 11 illustrates a system for stabilizing cardiac arrhythmiasconstructed in accordance with the principles of the present invention,where all system components are incorporated in a single housing.

FIG. 12 illustrates an alternative embodiment of a system forstabilizing cardiac arrhythmias according to the present invention,where the control circuitry, the electrical contacts, and thevibrational transducer are all provided in separate, implantablemodules.

FIG. 13 illustrates implantation of a device according to the presentinvention, where the device comprises a single housing which passeselectrical energy through the body to the heart from electrodes on thehousing to provide delivery of the electrical energy.

FIGS. 14A and 14B illustrate the implantation of an alternative deviceaccording to the present invention, where the device includes a singlesubcutaneous lead which is implanted into the body and which passeselectrical energy through the body to the heart from electrodes on thelead.

FIGS. 15A and 15B illustrate implantation of a device according to thepresent invention, where the device includes a pair of subcutaneousleads.

FIG. 16 illustrates implantation of a device according to the presentinvention, where the device includes a single (multielectrode)transvenous lead implanted into the heart.

FIG. 17 illustrates the combination of a vibrational energy transducerand electrical energy delivery paddles for external energy delivery.

DETAILED DESCRIPTION OF THE INVENTION

The present invention achieves improved treatment of cardiac arrhythmiasby exposing the heart, concurrently or sequentially, to two differentenergy sources at least comprising vibrational energy and electricalenergy. The separate energy sources are selected to stimulate orotherwise affect the same ion channels, different ion channels, orcombinations of the same and different ion channels. Such combinedstimulation of the ion channels using different energy sources providesenhanced treatment of arrhythmias, particularly allowing the use oflower electrical energy which is less painful and distressing to thepatient. It is contemplated, however, that in some instances higherelectrical energies typical of those presently employed indefibrillation may also be employed in combination with vibrationalenergy, where a more reliable termination of an arrhythmia may beachieved. More reliable termination of fibrillation would reduce theneed for multiple electrical energy deliveries for a single arrhythmiaepisode, thus reducing the patient's exposure to painful shocks andconserving battery power.

The present invention relies on directing vibrational energy,particularly ultrasound energy and electrical energy, into cardiactissue in order to terminate an arrhythmia. An understanding of thenature of ultrasound energy and biological tissue is of use.

Ultrasound in biological tissues is virtually exclusively a longitudinaltraveling wave, as illustrated in FIGS. 1A and 1B. The wave travels attypically 1.5 millimeters per microsecond, in a straight line unlessreflected or refracted. Ultrasound may be CW (continuous wave), meaningit is on all the time, or burst mode, comprising periods of ON timeseparated by lengths of OFF time. The lengths of the ON and OFF periodsmay be the same or different, and the total of the “on time” and “offtime” is referred to as the pulse repetition period (PRP). Asillustrated in FIG. 1, ultrasound waves do not come up to peak amplitudeinstantaneously. The number of cycles involved in the rise time and thefall time are approximately equal to the Q (quality factor) of thedevice. The period of an ultrasound wave is the time for one completecycle. The reciprocal of period is the frequency. Bursts may occur atany selected frequency, and the burst rate is defined as the pulserepetition frequency (PRF), which is the reciprocal of the pulserepetition period (1/PRP). The amplitude of the wave can be defined interms of pressure. In power applications, the magnitude of peak positivepressure is usually greater than that of the peak negative pressure. Thewaveform is slightly asymmetric due to non-linearities. Thesenon-linearities arise from different velocities of sound in the body asa function of signal strength, and are dependent on the distance oftravel through tissue and of course, amplitude.

From the above basic descriptors, other ultrasound parameters follow.The duty cycle is defined as the percent of time the ultrasound is inthe ON state. Thus, a continuous wave would have a duty cycle of 100percent. Intensity is the ultrasound power per unit area. Further commondefinitions are Ispta (intensity, spatial peak temporal average), theaverage intensity in the center of the beam over all time, and Isppa(intensity, spatial peak pulse average), the average intensity in thecenter of the beam averaged only over the duration of the pulse.

Two more parameters are the Mechanical Index (MI) and the Thermal Index(TI). MI is defined as the peak negative pressure in units of MPadivided by the square root of frequency in units of MHz. The parameteris defined for diagnostic ultrasound and reflects the ability ofultrasound to cause mechanical damage, across a wide range offrequencies. The FDA guideline for diagnostic ultrasound allows amaximum MI=1.9. TI for soft tissues is defined as the average power inthe beam in milliwatts times the frequency in MHz divided by 210. TIdefines the capability of ultrasound to create thermal bioeffects intissue, and a value of unity corresponds to a theoretical temperaturerise in normal tissue of one Centigrade degree. These expressions showimportant trends for ultrasound. For a given pressure, lower frequenciestend to result in greater mechanical bioeffects. Further, for higherfrequencies, there is a stronger tendency for greater thermalbioeffects.

An ultrasound beam is attenuated by the tissues through which itpropagates. Tissue motion has no effect on ultrasound attenuation. Atfrequencies below 5 MHz, attenuation in blood is negligible. Attenuationin myocardium, muscle, fat, and skin is approximately 0.3 dB per MHz percentimeter of propagation path. Consequently, a 1 MHz beam will sufferlittle attenuation through the body wall and heart. All frequencies ofultrasound do not propagate well through air; it is virtually totallyattenuated. The lungs and bowel gas essentially totally obstruct thebeam. Attenuation in bone is strongly frequency-dependent. Theattenuation at 1 MHz is in excess of 12 dB per centimeter, rising almostlinearly with frequency. At 100 kHz, attenuation is negligible.

Ultrasonic beams are highly dependent on the aperture of the radiatorand the frequency, and whether the beam is continuous wave burst mode. Asimple rule is that in the far field, the beam width is given by thewavelength divided by the aperture. Given the same sized apertures, alow frequency (Low f) beam might be almost isotropic (equal intensity inall directions) while a high frequency (High f) beam will be focused, asillustrated in FIG. 2. Further, the shape of the aperture will affectthe beam. FIG. 3 depicts high frequency beams from convex, planar, andconcave apertures, forming divergent, mildly focused, and sharplyfocused beams, respectively. In the far field, pulsed and continuousbeams have approximately the same profiles. In the near field, however,continuous beams are characterized by multiple peaks and valleys due toconstructive and destructive interference, respectively, of wavefrontsfrom across the aperture. (In the near field for short bursts ofultrasound, constructive and destructive interference is limited toemissions from smaller portions of the aperture, and consequently, nearfield emission profiles are more uniform.)

Referring now to FIGS. 4A and 4B, the present invention relies in parton directing ultrasound and other vibrational energy to the heart H inorder to stabilize cardiac electrical activity as generally discussedabove. In particular, for defibrillation, it is desirable to be able todirect the ultrasonic energy over as great a portion of the heartvolume, e.g., the aspect closest to the chest, as possible in order toassure maximum effectiveness. Usually, for defibrillation, the presentinvention will provide for directing the ultrasonic energy to at least50% of the cardiac tissue, preferably at least 75%, and more preferably90% or greater. Usually, for pacing treatment, the vibrational energywill be delivered to less than 50% of the heart. As the heart is locatedbeneath the body wall (BW), ribs R and sternum S, however, thevibrational transducer assembly (as described in greater detail below)must be properly located to deliver the energy. Bone and cartilagesignificantly attenuate the propagation of high frequency ultrasonicenergy, and the lungs L (which are filled with air) will totallyobstruct the transmission of such energy.

For the treatment of ventricular arrhythmias, it will generally bepreferred to implant a vibrational transducer assembly 10 either overthe ribs R, as shown in FIG. 5C, between or in place of the ribs Rand/or sternum, as shown in FIG. 5B, or perhaps less desirably under theribs R, as shown in FIG. 5A. When implanted beneath the ribs, thevibrational transducer assembly 10 will usually be placed over or spacedslightly anteriorly from the pericardium. Alternatively, but not shown,the transducer assembly may be implanted in the abdomen, either withinor outside of the peritoneal cavity.

For the treatment of atrial arrhythmias, the vibrational transducer ispreferably disposed to preferentially deliver the vibrational energy tothe atrial regions of the heart. Because of the different anatomicallocation of the atrium, it will be possible to place the vibrationaltransducer(s) either or both anteriorly or posteriorly on the patient.The anterior implantable locations may generally be the same asdescribed above with respect to FIGS. 5A-C, except that the preciseposition may be changed to overlie the atrium instead of the ventricle.Alternatively or additionally, the direction at which the vibrationalenergy is directed from the implanted device may also be modified topreferentially target the atrium as opposed to the ventricle. Particularposterior implantable locations are described in pending U.S. patentSer. application No. 10/869,776 filed Jun. 15, 2004 (now U.S. Pat. No.7,006,864), the full disclosure of which has previously beenincorporated herein by reference.

Referring now to FIG. 6, a first exemplary vibrational transducerassembly 10A comprises a quarter wave front surface matched device. Ahalf-wave thickness of piezo electric ceramic 12 is sandwiched betweenthin layer electrodes 14 having leads 17 and with a quarter-wavematching layer 16 disposed over the first surface. The piezo electricceramic 12 is positioned in a housing 18 with an air cavity 20 at itsrear surface. In this way, the quarter-wave matching layer 16 provides afront surface of the assembly 10A, and the edges and back of the housingneed only be strong enough to provide mechanical support. The air cavity20 will typically have a width of about 1 mm, and the thickness of theceramic and matching layer will vary depending on the desired frequencyof operation. Table 1 below shows the operational frequencies andthicknesses of the ceramic layer 12 and matching layer 16.

TABLE 1 Device Ceramic Matching Frequency Thickness Thickness (MHz) (mm)(mm) 2.0 1.0 0.37 1.0 2.0 0.75 0.5 4.0 1.5 0.25 8.0 3.0 0.10 20.0 7.5

The methods of the present invention likely result from the mechanicaleffects of ultrasound. As such, the maximum frequency might be on theorder of 1 MHz. From a structural point of view, at 0.10 MHz, the devicepackage thickness might be on the order of 30 mm thick, probably themaximum acceptable for an implant. If the device needs to be implantedover the ribs and/or sternum or placed externally, the lower frequenciesare preferred. At 0.25 MHz, the attenuation due to bone might beminimal, thus suggesting an operational frequency in the 0.10 to 0.5 MHzrange.

Operating below 0.25 MHz with a conventional quarter wave device may notbe especially advantageous due to the higher voltages needed to drivethe device. Also, as the device gets thicker, it becomes substantiallyheavier.

Not shown, the transducer assembly 10A may be substituted with a 1-3piezo-composite material instead of the ceramic. Piezo-compositematerial consists of piezoelectric ceramic posts in a polymer matrix.Such materials are thinner than the equivalent pure ceramic materialneeded to achieve a particular frequency and there is no need to providea matching layer. Thus, a simple high-voltage seal may be substitutedfor the matching layer 16 of FIG. 6. Suitable thicknesses for thepiezo-composite material are shown in Table 2 below.

TABLE 2 Device Frequency Piezo-composite (MHz) Thickness (mm) 2.0 0.751.0 1.5 0.5 3.0 0.25 6.0 0.10 15.0

Besides creating a thinner package, the piezo-composite materials haveanother significant benefit in that they can be easily curved,potentially to conform to anatomical features or optimize the transducerbeam profile. It must be remembered that any curvature will affect thefocal characteristics of the device.

Referring now to FIG. 7, a vibrational transducer assembly 10B may beformed as a variation on a Tonpilz transducer where a piezo drive 30(shown as a stack of piezo-elecetric material) induces ultrasonicvibration on a front vibrator 32. The package 34 provides the necessarytail mass for operation of the transducer assembly. Optionally, astructure (not shown) for retaining the front surface vibrator 32against the ceramic stack 30 and housing 34 may be provided. Strongvibrations of the surface vibrator may exceed the tensile strength ofthe ceramic and/or bonding material. Such transducer assemblies areparticularly well suited to operation at low frequencies, 0.1 MHz andbelow.

For defibrillation, the device of the present invention will require anaperture generating a relatively wide acoustic beam in order to deliverultrasonic or other vibrational energy over a relatively large portionof the heart. Due to biological constraints, the transducer may be inproximity to the heart, and as such, the heart may be in the near fieldof the acoustic beam. With typical human heart dimensions of 12 cm inlength and 10 cm in width, the ultrasonic or other vibrational energyaperture will typically be circular with a diameter on the order of 10cm, more preferably elliptical with long and short axes of 12 and 10 cm,and most preferably elliptical with the ultrasonic or other vibrationalenergy aperture slightly exceeding the dimensions of the heart to assuremaximal coverage of myocardium with therapeutic energy. It is recognizedthat many different sizes of devices might be required to meet the needsof different patient sizes.

Further variations on device design are possible. Specifically, recentlydeveloped high strain materials such as single crystal or polymerpiezo-electrics might be employed. In the case of the single crystals,current technology does not provide material with dimensions consistentwith the sizes projected to cover a significant fraction of the heart.Consequently, a mosaic structure of individual pieces or sections 40 ofpiezo electric material, as depicted in FIG. 8, might be employed. Thesections 40 are arranged within an ultrasonic radiative aperture 42 in acasing 44. The sizes of individual pieces would be consistent withcurrent manufacturing technology, currently approximately one inch onthe side. The single crystals may have individual signal generators,driving amplifiers, and/or impedance matching circuits for parallel orserial operation. Alternatively, the single crystals may be driven in asequential (multiplexed) manner by a single signal generator, poweramplifier, and matching layer. The single crystals may employ frontsurface impedance matching (quarter wave thicknesses) as used for theconventional piezo-electrics as depicted in FIG. 6. The mosaic ofindividual pieces may be mounted on a flat coplanar surface, or thedevices might be so mounted as to give the front surface of the deviceeither a concave or convex surface for better implantation under thepatient's skin. Likewise, the polymer devices might be flat or curved,as appropriate for acoustic coupling beneath the patient's skin. Polymerdevices probably will not require a front surface impedance matchinglayer, but may be backed with a high impedance backing layer to projectas much of the acoustic energy out into the patient as possible. Drivingmaterials for transducers may also include any other electro-mechanicalmaterial, one specific example being magnetostrictive materials.

The device may be driven with a high voltage and a high current. Afterappropriate electrical impedance matching, the current drain on thebattery may exceed the capability of the same. It is thus proposed tosegment the aperture into multiple individual pieces of piezoelectric,as depicted in FIG. 8 and as described above. In this case, each elementmay be driven by an individual power amplifier, impedance matchingcircuit, and signal generator (or a signal generator gated to individualdevices). Alternatively, the single crystals may be driven in asequential (multiplexed) manner by a single signal generator, poweramplifier, and matching layer. As such then, exposure of the heart wouldbe segmental. If, for example, the aperture consisted of 10 elements,operating with 5 cycles at 1 MHz, each element might be triggered every50 microseconds, allowing for an effective 10 percent duty cycle. Thiswould reduce the current demand on the battery by a factor of 10.

FIGS. 9A and 9B depict one possible circuit configuration for generatingserial bursts from the segmented aperture, and further depicts theinterlaced output from each of the individual elements within theaperture. It is possible to generate multiple bursts from every elementduring a small fraction of the cardiac cycle. The myocardium willeffectively experience simultaneous ultrasound exposure. Care must beexercised in the implementation of this concept to prevent excessivebeam spreading from the smaller elements and loss of far field signalstrength. Low frequency devices would be more prone to this problem thanhigh frequency devices.

Alternatively, the segmented aperture of individual elements of electromechanical material, or clusters of one to several posts of a piezocomposite material, may be driven in a phased sequence, so as to createan ultrasound beam in one of several particular directions. “Phasing”means that the driving signals applied to all elements or segments ofthe aperture have time delays such that the wavefronts from each elementor segment arrive at a designated tissue mass at the same time(constructive interference). Although the amplitude in this tissue masswill be greater due to the focusing effect of the phased aperture, thebeam may no longer cover the entire region of tissue requiringtreatment. Consequently, in rapid succession, on time scales very smallcompared to the time of the cardiac cycle, the beam may be directed tomultiple tissue masses in the region of treatment, so as to effectivelyuniformly expose the entire region with ultrasound.

Circuit configurations for operation in a phased array mode may be quitesimilar to the circuit configuration depicted in FIG. 9A. For phasedarray operation, all elements would be operative at the same time,albeit with different time delays. The burst generator would provide thedifferent time delays which would be directed to specificamplifiers/elements through the multiplexer (MUX). Multiple sets of timedelays would result in beams in multiple directions.

Instead of segmenting the aperture in a compact two-dimensional format,the aperture may be comprised of a series of segments or elements in alinear arrangement. Such an array of elements may be implanted or fixedexternally for directing vibrational energy to the heart from betweenthe ribs. Indeed, a second string of elements could be implemented insimilar format, for directing vibrational energy to the heart throughanother intercostal space, either above or below the first string ofelements. Alternatively or in conjunction, a string of elements may beimplemented over the sternum. Although there will be some attenuation ofthe ultrasonic beam, directing vibrational energy through the sternumwill assure a pathway to the heart unimpeded by lung tissue. The singleor multiple linear strands of aperture segments or elements can beelectrically driven in parallel or in serial format, or driven in aphased format for targeting of a specific region of the heart, or forsweeping the ultrasonic beam across a greater portion of the heart.

For pacing therapy, the device of the present invention may not requirean aperture for generating a wide acoustic beam since it is notnecessary for the acoustic beam to deliver energy to the majority of theheart. Thus, pacing may be accomplished by delivering vibrational energyfrom a portion of the transducer aperture using a segmental design, oralternatively, from a separate transducer aperture generating a narroweracoustic beam. If using a separate transducer, the separate transducermay be smaller in size and of a different shape. Thus, the invention maybe comprised of one or more that one transducer assembly, connected by acable (not illustrated).

It is assumed that the desired effect is a mechanical effect. Operatinga transducer in continuous wave mode creates a maximum thermal effectand a minimal mechanical effect. Operating in burst mode with a low dutycycle and a high amplitude minimizes thermal effects and maximizesmechanical effects. It is further believed, with some empiricalevidence, that high burst rates (and short burst lengths) provide theyet further enhancements to a mechanical effect. Consequently, apreferred design will be for shortest possible burst lengths, maximumamplitude, and duty cycle to the thermal limit.

The above paragraphs discussed some of the packaging considerations forthe transducer portion of the device. To summarize, the overhead on theaperture is expected to be minimal, perhaps adding 5 to 10 mm to thediameter of a device. The thickness of the device will be defined by thetype and the frequency. The electronics package (and battery) can becombined with the transducer or can be separately housed, with a cablebetween the two units.

FIG. 10 represents a block diagram of a possible electronics package forthe vibrational portion of the device. The sensor circuit would bemonitoring the heart and the power side of the system would generallyremain idle until such time an arrhythmia event were to occur. Thesensor circuits may be integral with the CPU. Once an event is detected,the CPU would trigger the burst generator which would generate apreprogrammed series of bursts, until such time as the heart hasreturned to normal rhythm. The electrical bursts would pass to a poweramplifier, an impedance matching circuit, and on to the transducer. Abattery would supply power for the typically digital circuits in theCPU, telemetry, sensor, and burst generator, the typically analogcircuits in the front ends of the sensor and amplifier, and to a voltageconverter which produces the high voltage for the output stages of theamplifier. Monitoring circuitry would provide feedback to the CPU aboutthe actual performance of the power amplifier and transducer(s).

The operational life of a defibrillator system may be expected to be onthe order of that for an implantable ICD. The operational life of apacing system may be on the order of a year or more progressing up to 5years. A battery volume similar to that used in an ICD is anticipated.The amplifier and impedance matching circuits might require on the orderof 25 cubic centimeters of volume, and the digital portions on the orderof 5 cubic centimeters. In all, it is reasonable to assume that thepackage could be implanted into the chest of a human. Use of arechargeable battery system utilizing transcutaneous inductive energytransmission may be beneficial.

The circuitry of FIG. 10 may be adapted to drive the associatedvibrational transducer under conditions which will impart vibrationalenergy to the heart so that the arrhythmia is terminated. In particular,the vibrational transducer may be operated under the conditionsspecified in Table 3. The device of the present invention may or may notallow for synchronization of the therapeutic ultrasound or vibrationalenergy burst to the cardiac cycle. In a first embodiment, once a rhythmabnormality is detected, the system will immediately initiate thepreprogrammed therapeutic protocol, irrespective of the time point onthe cardiac cycle. In a second embodiment, the system may trigger duringany time within prespecified intervals of the cardiac cycle. In yet athird possible embodiment, the system may initially be energized for apreprogrammed protocol, but then fall into a specified time interval ofthe cardiac cycle as normal rhythm is detected or anticipated.

The duration that the vibrational energy is delivered is a function ofthe transducer frequency, burst length (number of cycles), burst rate,and duty cycle. It is anticipated that the vibrational therapy might beapplied for a duration less than one complete cardiac cycle. It isfurther anticipated that the vibrational energy therapy might berepeated for more than one cardiac cycle.

TABLE 3 Cardioversion and Defibrillation Pacing Preferred More preferredMost preferred Most preferred Parameter Implementation ImplementationImplementation Implementation Frequency (MHz) 0.020–10.0 0.050–1.000.100–0.300 0.25–0.50 Burst length (cycles) <5000 <500 <50 <50 Burstrate (Hz) >10 ≧100 ≧100 Single burst Duty cycle (%) <50 <10 <5 100 No.of cardiac cycles as required <5 1 All Duration (msec) <200 <50 <20 <0.2MI <50 <25 <15 <2 TI <4 <1 <.1 <0.10 Myocardial Coverage (%) >50 >75 >90<20 Cardiac cycles from <10 <5 <2 0 or 1 sense to trigger

The apparatus of the present invention will also require electricalcontacts and circuitry for delivering electrical energy to the heart forcardioversion or defibrillation. The circuitry, electrical contacts, andother aspects of the system may generally be similar to the implantableand external defibrillators which are presently available and welldescribed in the medical and patent literature. For example, suitableexternal defibrillator circuitry and systems may be combined with thevibrational systems of the present invention and are described in U.S.Pat. Nos. 6,567,698; 6,047,212; 5,891,173; 5,879,374; 5,643,324;5,607,454; 5,593,428; 5,411,537; 4,825,871; and 4,198,963.

Similarly, power supplies and circuitries suitable for deliveringelectrical energy using the implantable apparatus of the presentinvention are described in U.S. Pat. Nos. 6,327,499; 6,292,691;6,282,444; 6,184,160; 6,085,116; 6,081,746; 6,076,014; 6,006,131;5,904,705; 5,899,923; 5,861,006; 5,755,742; 5,720,767; 5,540,721;5,514,160; 5,447,522; 5,439,482; 5,431,685; 5,413,592; 5,411,537; and5,407,444.

The full disclosures of each of these listed prior U.S. Patents listedin the paragraphs above are incorporated herein by reference.

The systems of the present invention may be adapted for total or partialimplantation or, alternatively, may be intended for external use only.The external systems may be configured in a manner similar to that forconventional electrical external defibrillators, typically including acontrol unit, external paddles or other electrical contacts for placingon spaced-apart locations on the patient's chest, and further includinga component for externally applying vibrational energy in either or bothanterior or posterior locations on the patient's chest.

Referring to FIGS. 11 and 12, alternative systems of the presentinvention which are implantable may include components disposed entirelywithin a common housing, as shown in FIG. 11, or components containedwithin a plurality of separate housings or modules (FIG. 12). A commonhousing 100 may include all internal power and control circuitrynecessary for operating the system. For example, circuitry 102 may beprovided for powering the unit, typically including a battery, circuitry104 may be provided for controlling vibrational transducer 106, andcircuitry 108 may be provided for controlling and powering electrodeleads 110. Electrode leads 110, in turn, may be configured either forsubcutaneous or intravenous implantation, or alternatively and notshown, the electrodes may be placed on the housing.

The cardiac stabilization system 120 illustrated in FIG. 12 includesseparately implantable components with housing 122 containing CPUcontrol and power circuitry for both electrical energy and vibrationalenergy, implantable leads 126, and a vibrational transducer housing 128.Each of these components may be separately implanted at differentlocations to optimize therapies according to the present invention.

Referring now to FIG. 13, a system 140 according to the presentinvention wherein all components are included in a single housing asshown implanted anteriorly over the lower rib cage. The system 140includes electrical contacts built into the housing and will typicallybe implanted so that these integrated contacts may directly activate theventricular or atrial aspect of the heart.

Systems 150 according to the present invention may include a singlesubcutaneous lead 152 containing both or either electrical orvibrational elements, as shown FIGS. 14A (front view) and 14B (sideview). Main housing of the system 150 will include the vibrationaltransducer and electrical energy components and be implanted in theanterior chest overlying the ventricular or atrial region of the heart.The single subcutaneous lead 152 may then be implanted subcutaneouslyparallel to the left anterior ribs as illustrated.

A defibrillation system 160 including a pair of implantable subcutaneousleads 162 as illustrated in FIGS. 15A (front view) and 15B (side view).As with system 150, the housing of system 160 will include thevibrational transducer and electrical energy components and may beimplanted to deliver the vibrational energy to the target region of theheart. As illustrated, the housing is implanted in an anterior region ofthe chest overlying the heart. The subcutaneous leads 162 containingboth or either electrical or vibrational elements are then positioned tobe implanted subcutaneously over the sternum to the right and parallelto the left anterior ribs as illustrated.

Referring now to FIG. 16, a system 170 according to the presentinvention comprises a transvenously implanted lead 172 which may beimplanted directly within an atrium or ventricle of the heart, in amanner conventional for implantable pacemakers and/or defibrillators.The housing 170 includes the vibrational transducer which may beimplanted in either or both an anterior or posterior region of the chestin order to deliver vibrational energy to the target ventricular oratrial region of the heart.

In the case of externally delivered vibrational energy, the transducerassembly may be a separate component or may be located in either or bothof the two electrical energy paddles, as depicted in FIG. 17. Thehousing 170 controls both the electrical energy paddles 172 and 174 andin this example the vibrational energy transducer 176 within paddle 174.The addition of coupling gel is necessary to delivery for bothelectrical and vibrational energies from paddles 172 and 174 to thepatient.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the appendedclaims.

1. A method for stabilizing cardiac arrhythmias, said method comprising:delivering controlled vibrational energy to the heart from a vibrationaltransducer disposed in a housing, wherein the vibrational energy isdelivered from the vibrational transducer through interveningnon-cardiac tissue; and delivering electrical energy to the heart,wherein the vibrational energy and electrical energy are delivered underconditions which terminate the arrhythmia, the housing is not in contactwith the heart, and the vibrational transducer operates above 100 kHz,wherein the vibrational energy and the electrical energy are deliveredat least partly simultaneously.
 2. A method as in claim 1, whereindelivering at least one of the controlled vibrational energy and theelectrical energy is performed by an implanted device.
 3. A method as inclaim 2, wherein both the controlled vibrational energy and theelectrical energy are delivered by an implanted device.
 4. A method asin claim 1, wherein delivering at least one of the controlledvibrational energy and the electrical energy is performed by an externaldevice.
 5. A method as in claim 4, wherein both the controlledvibrational energy and the electrical energy are delivered by anexternal device.
 6. A method as in any one of claims 2-3, wherein thedevice is implanted at least partially under the patient's ribs.
 7. Amethod as in any one of claims 2-3, wherein the device is implanted atleast partially in a gap between the patient's ribs.
 8. A method as inany one of claims 2-3, wherein the device is implanted at leastpartially over the patient's ribs.
 9. A method as in any one of claims2-3, wherein the device is implanted in the abdominal region.
 10. Amethod as in any one of claims 2-3, wherein the device is implanted inthe subcutaneous space of the anterior chest over the sternum.
 11. Amethod as in any one of claims 2-3, wherein the device is implanted in asubcutaneous space of the anterior chest over the ribs.
 12. A method asin any one of claims 2-3, wherein the device is implanted in asubcutaneous space of the posterior chest.
 13. A method as in any one ofclaims 1-3, wherein delivering the vibrational energy comprisessequentially energizing individual vibrational transducer segments,wherein at least some of the segments direct vibrational energy todifferent regions of the heart.
 14. A method as in any one of claims1-3, wherein delivering vibrational energy comprises sequentiallyenergizing individual vibrational transducer segments, wherein at leastsome of the segments direct vibrational energy to the same region of theheart.
 15. A method as in any one of claims 1-3, wherein the vibrationaltransducer consists essentially of a single piezo-electric disposed inthe housing with an air backing.
 16. A method as in any one of claims1-3, wherein the vibrational transducer comprises a piezo-compositematerial including piezo-electric ceramic posts in a polymer matrix. 17.A method as in any one of claims 1-3, wherein the vibrational energy hasa frequency in the range from 0.1 to 10 MHz, a burst length less than5,000 cycles, a burst rate less than 100 kHz, a duty cycle less than50%, a mechanical index less than 50, and a thermal index less than 4.18. A method as in any one of claims 1-3, wherein the vibrational energyis delivered to at least 50% of the heart.
 19. A method as in any one ofclaims 1-3, wherein the vibrational energy is delivered to less than 50%of the heart.
 20. A method as in claim 1, wherein the electrical energyis delivered externally at 360 Joules and below.
 21. A method as inclaim 1, wherein the electrical energy is delivered externally at 0.1Joule and above.
 22. A method as in claim 1, wherein the electricalenergy is delivered through electrodes implanted in the heart, whereinthe electrical energy is at 75 Joules and below.
 23. A method as inclaim 1, wherein the electrical energy is delivered through electrodesimplanted in the heart, wherein the electrical energy is at 100 μJoulesand above.
 24. A method as in claim 1, wherein the electrical energy isdelivered through electrodes implanted subcutaneously; wherein theelectrical energy is at 75 Joules and below.
 25. A method as in claim 1,wherein the electrical energy is delivered through electrodes implantedsubcutaneously, wherein the electrical energy is at 100 μJoules andabove.
 26. A method as in any one of claims 1-3, further comprisingdetecting an onset of an arrhythmia in a patient and initiating at leastone of delivering the controlled vibrational energy and the electricalenergy automatically in response to such detection.
 27. A method as inclaim 26, wherein the deliveries of both the controlled vibrationalenergy and the electrical energy are initiated in response to detectionof the arrhythmia.
 28. A method as in any one of claims 1-3, wherein thedelivery of at least one of the controlled vibrational energy andelectrical energy is initiated manually.
 29. A method as in claim 28,wherein the deliveries of both the controlled vibrational energy and theelectrical energy are initiated manually.
 30. A method as in any one ofclaims 1-3, wherein the vibrational energy is preferentially deliveredto a ventricular region of the heart.
 31. A method as in claim 29,wherein the electrical energy is preferentially delivered to aventricular region of the heart.
 32. A method as in any one of claims1-3, wherein the vibrational energy is preferentially delivered to anatrial region of the heart.
 33. A method as in claim 29, wherein theelectrical energy is preferentially delivered to an atrial region of theheart.
 34. A system for stabilizing cardiac arrhythmias, said systemcomprising: a vibrational transducer disposed in a housing and adaptedto deliver vibrational energy to the heart, wherein the vibrationaltransducer is adapted to deliver the vibrational energy to the heartthrough intervening non-cardiac tissue; electrical contacts adapted todeliver electrical energy to the heart; and control circuitry fordelivering at least one of the vibrational energy and the electricalenergy, wherein the housing is not in contact with the heart and thevibrational transducer operates above 100 kHz, wherein the vibrationalenergy and the electrical energy are delivered at least partlysimultaneously.
 35. A system as in claim 34, wherein the system isimplantable and the electrical contacts are adapted to directly engagethe heart.
 36. A system as in claim 34, wherein the system isimplantable and the electrical contacts are adapted to indirectly engagethe heart.
 37. A system as in claim 34 or 35, wherein the vibrationaltransducer operates at a frequency in the range from 0.1 to 10 MHz, aburst length less than 5,000 cycles, a burst rate less than 100 kHz, aduty cycle less than 50%, a mechanical index less than 50, and a thermalindex less than
 4. 38. A system as in claim 34 or 35, wherein thecontrol circuitry delivers electrical energy at 75 Joules and below. 39.A system as in claim 34 or 35, wherein the control circuitry deliverselectrical energy at 100 μJoules and above.
 40. A system as in claim 34,wherein the vibrational transducer and the electrical contacts areadapted to externally engage a surface of the patient's skin.
 41. Asystem as in claim 34 or 40, wherein the vibrational transducer operatesat a frequency in the range from 0.1 to 10 MHz, a burst length less than5,000 cycles, a burst rate less than 100 kHz, a duty cycle less than50%, a mechanical index less than 50, and a thermal index less than 4.42. A system as in claim 41, wherein the control circuitry deliverselectrical energy at 360 Joules and below.
 43. A system as in claim 42,wherein the control circuitry delivers electrical energy at 0.10 Jouleand above.
 44. A system as in claim 34, wherein the control circuitrydetects an onset of an arrhythmia and activates the vibrationaltransducer and delivers electrical energy in response to such detection.45. A system as in claim 34, wherein the control circuitry is manuallytriggered to activate the vibrational transducer and deliver theelectrical energy.
 46. A system as in claim 34, wherein the delivery ofvibrational energy is commenced prior to commencing the delivery ofelectrical energy.
 47. A system as in claim 34, wherein the delivery ofelectrical energy is commenced prior to commencing the delivery ofvibrational energy.
 48. A system as in claim 34, wherein the vibrationaltransducer and the control circuitry are packaged in a commonimplantable housing.
 49. A system as in claim 34, wherein the electricalcontacts are adapted to form a part of the exterior of the commonhousing.
 50. A system as in claim 34, wherein the electrical contactscomprise subcutaneously implantable leads.
 51. A system as in claim 34,wherein the electrical contacts comprise transvenously implantableleads.
 52. A system as in claim 34, wherein the vibrational transducer,the electrical contacts, and/or the control circuitry are packaged inseparately implantable housings, further comprising cables forconnecting the housings.
 53. A system as in claim 34, wherein thevibrational transducer consists essentially of a single piezo-electricdisposed in the housing with an air backing.
 54. A system as in claim34, wherein the vibrational transducer comprises a piezo-compositematerial including piezo-electric ceramic posts in a polymer matrix. 55.A system as in claim 34, wherein the vibrational transducer comprises aplurality of separately driven segments, wherein the segments arearranged to sequentially direct vibrational energy to different regionsof the heart when the system is implanted.
 56. A system as in claim 34,wherein the vibrational transducer comprises a plurality of separatelydriven segments, wherein the segments are arranged to sequentiallydirect vibrational energy to the same region of the heart when thesystem is implanted.
 57. A system as in claim 34, wherein thevibrational transducer is adapted to preferentially deliver vibrationalenergy to a ventricular heart region when implanted.
 58. A system as inclaim 34, wherein the vibrational transducer is adapted topreferentially deliver vibrational energy, to an atrial region of theheart when implanted.
 59. A system as in claim 34, wherein the controlcircuitry comprises sensor elements for detecting onset of an arrhythmiaand for synchronizing the delivery of vibrational and electrical energyin response to such detection.
 60. A system as in claim 59, wherein thecontrol circuitry further comprises a power amplifier, an impedancematching circuit, and a signal generator, for each segment of thevibrational transducer.
 61. A system as in claim 60, wherein the controlcircuitry further comprises a battery or a remotely rechargeablebattery.
 62. A system as in claim 61, wherein the control circuitryfurther comprises a transmitter and/or receiver for communication withan external controller.